The thermal printing process is conducted by selectively heating pixel-sized areas within a color patch of a dye donor web until the dye melts or vaporizes and is transferred to a dye receiver where it is deposited and solidified. The quantity of dye transferred and the resulting print density is determined by many factors including the amount of dye on the donor material. Conversely, a variation in print density can be caused by irregularities in the dye layer of the donor material. The state of manufacturing technology today is such that the dye coated donor material is occasionally defective or has defective patches. Defective donor material within a color patch will produce a defective print which requires remaking. Using defective donor wastes both time and receiver material.
If the location of defective color patches along the donor web could be marked, when a mark signifying a defective color patch is sensed during printing, the defective color patch, or a series of color patches containing the defective one could be passed over in the printing process. This would eliminate defective prints, speed the printing process, and decrease wasted receiver material. Accordingly, it will be appreciated that it would be highly desirable to identify the defective areas in the donor web during manufacturing and to detect the marked area during printing so that defective areas can be bypassed.